The dynamics of explosive boiling of a 2-propanol layer of variable thickness on a Si substrate heated by a nanosecond KrF excimer laser was studied using a contact photoacoustic technique. The transition from acoustic generation at a free Si boundary to that at a rigid alcohol/Si boundary accompanied by a sharp increase of acoustic generation efficiency was found above a laser fluence threshold of 0.17 J/cm2 and a liquid layer thickness greater than 0.25 μm due to subnanosecond near-critical explosive boiling of the superheated liquid layer near the hot absorbing Si substrate. The gradual increase of the photoacoustic response of the superheated alcohol with increasing thickness of the liquid film at fluences above the explosive boiling threshold was attributed to a diffraction effect due to the fluence- and time-dependent increase of the area undergoing explosive boiling. A model describing photoacoustic generation and subsequent lift-off of the entire liquid layer in this experimental “thin transparent liquid layer/solid absorbing substrate” geometry under near-critical explosive boiling conditions has been proposed.

Semiconductor opening switches (SOS) are able to interrupt currents at density levels of up to 10 kA/cm2 in less than 10 ns, operate at repetition rates up to 1 kHz, and possess lifetimes of more than pulses. If stacked, SOSdiodes can hold off voltage levels up to several 100 kV. They are therefore ideal for the design of compact high voltage pulse generators of the GW-class for industrial applications. The aim of this work was to improve our understanding of the opening process in a semiconductor diode of SOS-type with a doping profile of structure, obtainable through diffusion from the surfaces. To simulate the physical processes inside this diode the code POSEOSS was developed. It contains a detailed physical model of charge carrier transport under the influence of density gradients and electric fields and considers all relevant generation and recombination processes. It possesses a large degree of flexibility and is easy to use, and thus allows to carry out parameter studies to determine the influence of different physical quantities, such as doping and impurity levels, on the performance of the device. When applying the code some interesting results concerning the plasma dynamics during the opening process in the switch have been found. In particular, using realistic values for the charge carrier mobility, it was found that the opening process starts first at the boundary. Also it has been possible to derive the physical conditions for the occurrence of the SOS-effect. Based on the simulation results a simplified SOS equivalent circuit model has been developed. This model can be used in the circuit simulation program PSPICE. A pulse generator scheme based on inductive storage is proposed, in which power multiplication is achieved by unloading the inductors, previously charged in series, in parallel. This scheme can be considered as the inductive equivalent of a Marx-generator. PSPICE simulations of such a scheme based on semiconductor opening switches are presented. The theoretical results have been compared to measurements obtained with a simple experimental set-up using two 100 kV SOS-switches. The measurements showed good agreement with the simulation results. Further improvements seem possible by adapting the SOS device structure to the specific generator circuit.

The effect of a pre-deposited ultrathin film of indium on the deposition of cobalt on Cu(111) has been studied by an in situ combination of medium energy electron diffraction,scanning tunneling microscopy, and Auger electron spectroscopy. Pre-deposited indium allows cobalt to deposit in layer-by-layer growth, in contrast to the three-dimensional growth observed without the indiumsurfactant. The surfactant effect is connected to the surface alloys, and that form upon indium pre-deposition. Initial cobalt nucleation processes and indium segregation during cobaltdeposition are also discussed.

Lotus-type porous copper is a porous medium made of copper that contains many straight pores. To effectively employ lotus-type porous copper as a heat sink, it is necessary to clarify the pore effect on the thermal conductivity of lotus copper. This article describes an experimental and analytical investigation on the effective thermal conductivities of lotus copper parallel and perpendicular to the pores. The lotus copper displayed anisotropy of the effective thermal conductivity. The effective thermal conductivity perpendicular to the pores was lower than that of the parallel ones and was 40% that of lotus copper material with porosity ε of 0.4. Experimental data for showed good agreement with analytical results derived from the assumption that heat flow through the cross-sectional area parallel to the pore axis is proportional to (1−ε). Experimental data for showed good agreement with the analytical results derived from the assumption of orthorhombic symmetry and with the numerical results under a uniform staggered array with a nonuniform pore diameter.

Plasma-enhanced atomic layer deposition (PE–ALD) is a promising technique to produce high quality metal and nitride thin films at low growth temperature. In this study, very thin (<10 nm) low resistivity (350 μΩ cm) cubic TaN Cudiffusion barrier were deposited by PE–ALD from and a plasma of both hydrogen and nitrogen. The physical properties of TaN thin films including microstructure, conformality, roughness, and thermal stability were investigated by various analytical techniques including x-ray diffraction, medium energy ion scattering, and transmission electron microscopy. The Cudiffusion barrierproperties of PE–ALD TaN thin films were studied using synchrotron x-ray diffraction, optical scattering, and sheet resistance measurements during thermal annealing of the test structures. The barrier failure temperatures were obtained as a function of film thickness and compared with those of PE–ALD Ta, physical vapor deposition(PVD) Ta, and PVD TaN. A diffusion kinetics analysis showed that the microstructure of the barrier materials is one of the most critical factors for Cudiffusion barrier performance.

A layer containing an average of 1.0 monolayer (ML) of adventitious carbon and averages of 1.5 ML and 1.9 ML of hydroxide was determined to be present on the respective O-terminated and Zn-terminated (0001) surfaces of ZnO. A diffuse low-energy electron diffraction pattern was obtained from both surfaces.In situcleaning procedures were developed and their efficacy evaluated in terms of the concentrations of residual hydrocarbons and hydroxide and the crystallography,microstructure, and electronic structure of these surfaces.Annealing in pure oxygen at reduced but did not eliminate all of the detectable hydrocarbon contamination. Annealing for 15 min in pure at and caused desorption of both the hydrocarbons and the hydroxide constituents to concentrations below the detection limits of our x-ray photoelectron spectroscopy instrument. However, thermal decomposition degraded the surface microstructure. Exposure of the surface to a remote plasma having an optimized 20% He mixture for the optimized time, temperature, and pressure of 30 min, and 0.050 Torr, respectively, resulted in the desorption of all detectable hydrocarbon species. Approximately 0.4 ML of hydroxide remained. The plasma-cleaned surface possessed an ordered crystallography and a step-and-terrace microstructure and was stoichiometric with nearly flat electronic bands. A 0.5 eV change in band bending was attributed to the significant reduction in the thickness of an accumulation layer associated with the hydroxide. The hydroxide was more tightly bound to the ZnO(0001) surface; this effect increased the optimal temperature and time of the plasmacleaning process for this surface to and 60 min, respectively, at 0.050 Torr. Similar changes were achieved in the structural, chemical, and electronic properties of this surface; however, the microstructure only increased slightly in roughness and was without distinctive features.

An energy deposition model for electrons in air that can be useful in microdosimetric applications is presented in this study. The model is based on a Monte Carlo simulation of the single electron scattering processes that can take place with the molecular constituents of the air in the energy range 10–10 000 eV. The input parameters for this procedure have been the electron scattering cross sections, both differential and integral. These parameters were calculated using a model potential method which describes the electron scattering with the molecular constituent of air. The reliability of the calculated integral cross section values has been evaluated by comparison with direct total electron scattering cross-section measurements performed by us in a transmission beam experiment. Experimental energy loss spectra for electrons in air have been used as probability distribution functions to define the electronenergy loss in single collision events. The resulting model has been applied to simulate the electrontransport through a gas cell containing air at different pressures and the results have been compared with those observed in the experiments. Finally, as an example of its applicability to dosimetric issues, the energy deposition of 10 000 eV by means of successive collisions in a free air chamber has been simulated.

We describe in detail the detection of deflagration of trinitrotoluene (TNT) deposited on a piezoresistive microcantilever and point out its possible use for explosive-vapor detection. The deflagration of TNT causes the cantilever to bend (due to released heat) and its resonance frequency to shift (due to mass unloading). Explosive vapors provide unique responses that are absent for “interferences” such as water or alcohol vapors. The proposed sensor makes possible a sensitive, miniature explosives detection device that may be deployed in large numbers. The minimum amount of TNT detected on the cantilever depends on the cantilever dimensions and was ≈50 pg for the batch of cantilevers used.

In this work, we develop a numerical simulation method to characterize the photonicproperties of photonic crystals made of either dielectric or magnetic materials. Due to the magnetic materials in the photonic crystals, not only the dielectric but also the magnetic permeability functions vary periodically with position. Thus, a master equation is needed. The simulation method based on the existing algorithm developed for periodic media with uniform magnetic permeability [Johnson and Joannopoulos, Opt. Express 8, 173 (2001)] is further modified for the present case. We then use the modified numerical simulation method to investigate the photonicproperties, such as the dispersion relation,photonic band gap, and electromagnetic field distribution, of some typical photonic crystals which possess analytic expression or well-known photonicproperties. A good match between the simulated and the analytic results is obtained. This fact shows that the modified numerical simulation method can be used to explore electromagnetic waves in both dielectrically and the magnetically periodic media.

A study of N doping using and NO sources on ZnO, which may prove important for the N doping of oxide materials, was performed by investigating the doping processes of N atoms by each source together with the various properties for the grown N dopedZnOfilms. was employed as the radio-frequency (rf) plasma source to produce radical species that could effectively incorporate N atoms above into ZnO, which was similar to N doping using as the source. In contrast, it was found that the ZnOfilmsdoped with a N concentration above were easily obtained using a gas flow of NO. The N concentration could be controlled systematically by the simultaneous gas flow of NO and sources. The basis of N doping using a NO source could be related to the free radical characteristic of NO molecular. This idea was proposed from the results that the N concentrations doped to ZnO using a gas flow of and which have the characteristics of neutral and nonreactive molecules in air, were in the ranges from to Further, our investigations clarified that the structural, optical, and electrical properties for the N dopedZnOfilms were not quite dependent on the and NO sources used as N dopants. This work proposes that NO is a promising source as a N dopant that can be employed without using a rf plasma source in the application of physical vapor deposition techniques that are indispensable for producing radical species through a rf plasma source to achieve the efficient incorporation of N atoms when and sources are used as N dopants.

Films of well-ordered crystalline copper oxide (CuO) nanofibril arrays were synthesized using a procedure involving electrodeposition followed by a gas-solid reaction. Analyses showed that the nanocrystalline CuO nanofibrils with a mean length of 8 μm have an average density of Photoluminescence measurements showed a main peak in the visible light band at 410 nm, and the band gapenergy was estimated to be 1.67 eV. It was found that the film of aligned CuO nanofibrils has typical Fowler–Nordheim plots in the follow-up electron field emission test. Typical turn-on voltage was detected at ∼6 V/μm with an emission area of 1 mm2. The Fowler–Nordheim model was employed to analyze the data obtained. The work function of the nanofibrils was estimated to be in the range of 4.1–4.3 eV.

Gradient index lenses were formed in a liquid-filled cavity supporting an ultrasonic standing wave. The constructed devices acted as diverging lenses or axicon lenses, depending on whether the center or edge region is interrogated. The focal length of the diverging lens was controllable with the frequency and amplitude of applied ultrasound from −100 mm to negative infinity. Experiments and models suggest that the primary process contributing to lensing is the steady-state density component of the finite-amplitude standing wave; sound amplitudes up to 150 MPa were calculated in glycerin, corresponding to a maximum contrast in the refractive on the order of 0.1%. This amplitude was also sufficient to move high index nanometer-scale particles via an acoustic radiation force and thereby create larger refractive index gradients. The segregation of suspended nanoparticles was found to enhance the lensing effects that occurred in the pure fluids. Concepts are also explored to manipulate the particle distribution in order to create converging lenses and/or other desirable optical components.

Ge-based photodetectors operating in the low loss windows (1.3–1.6 μm) of silica fibers are highly desirable for the development of optical interconnections on silicon-on-insulator substrates. We have therefore investigated the structural and optical properties of Ge thick films grown directly onto Si(001) substrates using a production-compatible reduced pressure chemical vapor deposition system. We have first of all evidenced a Ge growth regime which is akin to a supply-limited one in the 400–750 °C temperature range The thick Ge layers grown using a low-temperature/high-temperature approach are in a definite tensile-strain configuration, with a threading dislocation density for as-grown layers of the order of (annealed: The surface of those Ge thick layers is rather smooth, especially when considering the large lattice mismatch between Ge and Si. The root-mean-square roughness is indeed of the order of 0.6 nm (2 nm) only for as-grown (annealed) layers. A chemical mechanical polishing step followed by some Ge re-epitaxy can help in bringing the surface roughness of annealed layers down, however (0.5 nm). The Ge layers produced are of high optical quality. An absorption coefficient alpha equal to 4300 cm−1 (3400 cm−1) has indeed been found at room temperature and for a 1.55-μm wavelength for as-grown (annealed) layers. A 20-meV band-gap shrinkage with respect to bulk Ge is observed as well in those tensile-strained Ge epilayers.